Shrink film has been used for years to encapsulate articles. The shrink film must be able to shrink sufficiently to provide a smooth consistent coating. Previously, shrink films have been polyolefins and polyolefin blends which were and are used extensively in the food and packaging business to protect and preserve articles, such as food. One problem with polyolefin and polyolefin film blends is the difficulty of printing on the film. For printing to be successful, the films must provide a surface that will accept printing. Additionally the films must have sufficient tensile modulus to withstand the rigors of the printing process. Many polyolefin shrink films do not have the tensile strength to withstand gravure printing.
Shrink film has also been used for encapsulating cylindrical articles such as batteries. Polyvinyl chloride (PVC) films provide acceptable shrinkages of about 40%. However, PVC shrink films have a problem with heat stability. After forming the shrink film, the film should not shrink prematurely. Often, after formation, the film may be exposed to elevated temperatures, such as in transport. Another problem with PVC shrink films is recent concerns over the environmental impact of PVC film. Concern regarding potentially the adverse effect of halogens on the ozone layer has lead to efforts to provide halogen free shrink films.
Batteries are typically encapsulated by shrink films. The film must shrink sufficiently to encase the battery. A problem with encapsulating batteries and any other cylindrical article is end puckering. End puckering occurs when the shrink film does not shrink sufficiently to provide a smooth encapsulating film at the ends of the battery or the article being encapsulate, and the film folds over itself and forms a “pucker.” This puckering is unacceptable to consumers and therefore the manufacturer.
Battery encapsulating is done at very high speeds. The speed of the labeling is often more that 700 labels applied per minute. It is difficult for typical shrink film labels to work under such high speed conditions.